STAGES OF LABOR
Although labor is a continuous process, it is divided into four functional stages because each has differing physio-logical activities and requires differing management.
The first stage of labor is the interval between the onset of labor and full cervical dilation (10 cm). The first stage is further divided into two phases: (1) The latentphase of labor encompasses cervical effacement and early dilation, and (2) the active phase of labor, during which more rapid cervical dilation occurs, usually begin-ning at approximately 4 cm.
The second stage of labor encompasses complete cer-vical dilation through the delivery of the infant.
The third stage of labor begins immediately after delivery of the infant and ends with the delivery of the placenta.
The fourth stage of labor is defined as the immediate postpartum period of approximately 2 hours after deliv-ery of the placenta, during which time the patient under-goes significant physiologic adjustment.
Table 8.1 outlines the duration of various stages of labor, as first described in the research by Emmanuel Friedman, and Figure 8.5 represents this information graphically, known as the Friedman curve. New data, derived since the advent of epidural labor analgesia, suggest that the maximum slope of the normal labor curve during active phase may actually be slightly less steep.